Apparatus for controlling flame propagation in internal-combustion engines



Filed Sept. 21, 1948 fJuly 28, 1953 B c FISHER 2,646,782

APPARATUS FOR COTRLLING FLAME PROPAGATION IN INTERNAL-COMBUSTION ENGINESA 3 Sheets-Sheet 1 4g 3l l52 2 BERNARD CJTISHER BY i, f//

July 28, 1953 B. c. FISHER f APPARATUS FOR coNTRoLLrNG FLAME PROPAGATIONIN INTERNAL-,COMBUSTION ENGINES 3 Sheets-Sheet 2 Filed Sept. 21, 1948lNvENToR BERNARD C. FISHER ATTORNEY July 28, 1953 B. c. FISHER 2,646,782

APPARATUS FOR CONTROLLING FLAME PROPAGTION IN INTERNAL-COMBUSTIONENGINES Filed Sept. 21, 1948 3 Sheets-Sheet 3 INVENTOR BY )4 y ATTORNEYI BERNARD Cfsm-:R

Patented July 28, 1953 UNITED STATES PATENT OFFICE APPARATUS FORCONTROLLING FLAME PROPAGATION IN BUSTION ENGINES 8 Claims.

This invention relates to internal combustion engines and especially toa means and a method for controlling the name propagation in thecombustion chambers of such engines.

This application is a continuation in part of my prior filedapplications, Serial No. 644,859, filed February 1, i946, now Patent No.2,534,860, issued December 19, 1950, and Serial No. r152,165, l'ed June3, i947, now Patent No. 2,545,546, issued March 20, 1951.

It has always been extremely difficult in the operation of internalcombustion engines to control the flame propagation in the combustionchambers thereof so as. to get the maximum driving force against thepistons during the proper portion of the power cycle. Many attempts havebeen made to solve this problem without great success. Among these hasbeen the practice of providing special fuel mixtures which act to delaythe burning of the mixture, so as to distribute the explosive force overa larger portion of the pistons power stroke. Up to the present timethese special fuel mixtures appear to give the best results. I havediscovered, however, that by a different proportioning, manipulation,and arrangement of the fuel and oxygen supply for the engine during thetime the fuel is introduced into the combustion space and compressedtherein, I can control the iiame propagation of the fuel mixture in amanner far better than has ever been done before and without the use ofany special fuel mixtures, and I can accomplish this by the applicationto the engine of a simple inexpensive device. In fact my inventionpermits the use of fuels hitherto thought unsuitable for use in aninternal combustion engine.

It is, therefore, the principal object of the in vention to provide amethod and a means for automatically controlling name propagation in aninternal combustion engine, so as to obtain A YA still further object ofthe invention is to provide a spark plug which when applied to an enginewill permit the accomplishments ci 'the objects in the last twoParagraphs abv.

INTERNAL-COM- A further object of the invention is to provide a meansand a method for operating an internal combustion engine whereby theengine may be operated with the ignition distributor at a lixed positionor with any desired arrangement of ignition control.

The invention has been illustrated in the accompanying drawingsy inwhich:

Figure 1 is a sectional side elevation of a portion of a highcompression engine designed for carrying out the invention.

Figure 2 is an enlarged sectional side elevation oi a portion of thespark plug of the engine of Figure 1 showing the construction of thevalve therein.

Figure 3 is a bottom plan view of the inner barrel of the spark plug ofFigure 1showing the valve seat and ducts leading to the air lter.

Figure 4 is an enlarged fragmentary perspective view of the air iilterused in the plug shown .in Figures 1 to 3.

Figures 5, 6, and 7 are schematic sectional views of the firing space inthe inner or electrode end of the sparkY plug of Figure 1 which may beused to illustrate the principles of ther invention.

Figures 8 and 9 are a fragmentary sectional side elevation and 'a bottomplan view, respectively, of a modified form of spark plug incorporatingthe invention. Y

Figures 10 and 11 are a sectional side elevational vieW and a sectionalplan View, respectively, of a modified form of spark plug from thatshown in Figure 1, by means of which mechanical ignition adjustingdevices may be eliminated, Figure 11 being taken on the line H-ll ofFigure 10.

Figures 12 and 13 are a sectional elevation and bottom plan View,respectively, of a modied form of certain parts of the spark plug ofFigure l0.

Figure 14 is a side elevation, partly in section, of another modifiedform of the invention; and Figure 15 is a sectional plan view of theplug of Figure 14, takenon the line llil5 of Figure 14.

In carrying out the invention I admit oxygen to the combustion space ofan internal combustion engine at the same time that the fuel mixture isintroduced therein and confine the oxygen during the compression stroketo a space adjacent the sparking electrodes, anad I control the flamepropagation of the explosive mixture in the cylinder by the properrelation between the amount of oxygen admitted and the configuration andsize of the space in which it is confined. I have found that aconvenient way to admit the oxygen is through a suitable duct in thespark plug of the engine, the inner end of which also provides aconvenient means for defining the above-mentioned space adjacent theelectrodes. I have, therefore, illustrated the invention in connectionwith an engine having a specially designed spark plug for carrying outthe objects of the invention, although I wish it to be understood thatthe features for admitting and controlling the auxiliary oxygen need notbe incorporated in the spark plug, but may, if desired, be a part of theengine head or may be furnished by means of an attachment thereto.

In Figure 1 I have shown an engine of the four cycle type having acylinder l in which a piston 2 is mounted for reciprocation in the usualmanner. I'he head 3 is provided with the usual compartments 4 for thecooling fluid 5, and in the top of the head is provided the usual tappedhole S for the specially constructed spark plug 'I which is providedwith a cylindrical end 8 threaded to screw into the hole 6.

The spark plug 'I has a shell 9 formed of two different outer diameters,the smaller diameter portion forming the cylindrical end 8 and theremainder forming an open-ended housing I for the components of theplug. A shoulder II is formed between these two portions and seats upona gasket I2 when the plug is screwed into place for making a gas-tightconnection with the engine. The other end of the housing Il! isthickened and has its outer circumference formed into a hexagon nut I3to which a wrench may be applied for screwing the plug into position.

The inner wall of the shell 9 has three portions of different diameters.The rst portion I4 of largest diameter has a diameter only slightlysmaller than the outside diameter of the housing it to form a thin wallfor the housing. This first portion of the inner wall terminates in ashoulder I5 at the inner edge of which the second portion I6 ofintermediate diameter commences. This portion IE denes a portion of thevalve chamber, (to be later described) and is relatively short,terminating in a shoulder H at the inner edge of which the third portionI8 of the inner wall commences. This portion is enough smaller indiameter than the threaded end 8 of the shell 9 to provide suiiicientstrength for the cylindrical end 8 of the plug.

The end of the inner portion I8 adjacent the shoulder VI is threaded toreceive a barrel I9 the outer surface of which has portions of twodiiferent diameters 29 and 2 i to conform generally in length and sizeto the portions I4 and I6 and I8, respectively, of the shell 9, theportion ZI being threaded to screw into the portion I8 of the shell 9.

Between the two portions 29 and 2I of the barrel I9 is a shoulder 23 theouter circumference of which has a rim 24 which extends axially of thebarrel and bites into the metal of the shoulder I5 in the shell 9 toform a gas-tight joint therebetween when the barrel is screwed intoplace.

The barrel I9 has a bore of two diameters: an outer end portion 25 andan inner end portion 26 of reduced diameter. Between these two portionsis provided a sloping shoulder 21 against which is seated the enlargedcentral portion 28 of the spark plug insulator 29 which may be of theusual design and may be made of porcelain or other suitable ceramic,having an elongated post 39 extending outwardly of the plug from iii theenlarged portion 28 and tapering to a smaller diameter from the enlargedportion towards the inner end of the plug, terminating at a pointsomewhat within the inner end of the barrel I9.

The insulator 29 has the usual small diameter bore extending through itfrom end to end in which is cemented the central electrode 3l of thespark plug. This electrode terminates at its inner end just about evenwith the inner end of the shell 9, in the example illustrated, andcooperates with a grounded electrode 32 which is welded to the end 8 ofthe shell 9 and extends diametrically towards the center of the plugwith its end spaced slightly from the end of the electrode 3|, so as toprovide a gap for a spark to jump.

The other end of the central electrode 3! terminates in a cap 33 whichmay be or" the usual design for attaching the wire to the plug from thedistributor of the engine.

A gland nut 35i is threaded into the open outer end of the barrel I9,the outer end of the portion 25 of the bore being threaded for thatpurpose. The inner end or" the gland nut is tapered to conform to thetapered surface of the enlarged portion 28 of the insulator 29, so as tohold the insulator in place when the nut is screwed into place, suitablesoft metal washers 3@ and 31 being provided adjacent the shoulder 2'!and the tapered end 35 of the nut 34, to make a gas-tight joint.

The rim 2Q, on the shoulder 23 of the barrel I9 is designed to separatethe shoulders 23 and I5 a distance just suflicient to form a valvechamber 38 in which operates a valve 39, which is preferably a fiat ringof stainless steel.

The portion I6 of the inner wall of the shell 9 is enough larger indiameter than the outer diameter of the portion 2! of the barrel I9 toprovide space for a light coil spring 40 which may preferably be ofstainless steel to resist rust and heat and which is under slightcompression between the valve ring 39 and the shoulder il of the shell 9and tends to maintain the valve ring against the shoulder 23 of thebarrel I9.

In the portion 29 of the barrel I9, a short distance from the rim 24, Iprovide a groove 4I which may extend completely around the circumferenceof the barrel and in which is positioned a lter 42 formed of a suitablematerial having many interstices to permit the passage of a gas butpreventing the passage of foreign particles which might otherwise passinto the engine cylinder.

I prefer to make the lter out of wire mesh and I have found that asuitable number of ne braided Phosphor bronze or inconel wires may becompressed into a cross-section to conform with the groove, cut off atthe proper length and wrapped around the groove with the ends abutting.A lfragment of such a filter is shown in Figure 4.

Small holes or ducts i3 are formed in the barrel I9 and extend betweenthe shoulder 23 and the groove 4I, these holes being preferably two innumber and being diametrically positioned with respect to the barrel.The arrangement is such that the valve ring 39 covers the holes 43 whenseated against the shoulder 23.

The diameter of the portion 20 of the barrel I9 is slightly smaller thanthat of the portion I4 of the shell 9 so as to provide a space or duct44 through ywhich air may pass into the groove 4I, and the lter 42 mayhave a radial di'- mension sufficient to provide a press fit within 7found that burned gasses pass only about onethird of the Way through theduct 45.

At the proper time, at the end of the proper stroke, the exhaust valveopens and the burned gasses rush out of the combustion chamber, aided bythe piston which has begun to move into the cylinder again. When theexhaust valve opens, the pressure within the combustion chamber dropsfar below the extremely high pressure created therein by the explosion.Since the air in the valve chamber 38 is under this much greaterpressure, some of it will be forced through the duct 45 and through thespace 46 into the combustion chamber. Any air left compressed in theinnermost portion of the space 46 joins this pure air in flushing theburned gasses out of the space 46 and away from the electrodes 3l and 32and again producing a cooling effect upon the electrodes and associatedparts. When the exhaust valve closesI at the end of the exhaust stroke,the cycle is ready to be repeated again with another intake stroke.

Consider now what will happen when load and speed conditions of theengine change. Assume for a predetermined condition of load and speedthat the region in the firing space 46 which the flame front has toreach before the blow-torch effect is obtained is represented by theline 49. Suppose now that the load is increased as, for instance, in anautomobile, when the automobile starts to climb a hill, and that thiscondition is met by opening the throttle for supplying more fuel to theengine. Since more fuel mixture enters the cylinder at the intakestroke, the compression in the cylinder will rise and it will be seenthat the various gradations of the mixture of fuel and air will besqueezed farther into the space 46, so that now the lines 41 and 52 mayassume the positions indicated in Figure 6. Thus it will now take longerfor the llame front from the spark to reach the region of line 49 andthe ignition is effectively retarded, which is what is desired when theload is increased, as is well known.

If the load should decrease and a smaller amount of fuel be admitted bythe throttle, the compression also decreases, thus permitting thestratified fuel mixture to spread out in the space 46 with the resultthat the line 49 may now be much closer to the spark, as indicated, forinstance, in Figure 7, requiring less time for the flame front to reachit and thus effectively advancing the ignition, which is again what isdesired for this condition.

Now assume again that the normal conditions prevail which produce theeffect indicated in Figure and that the speed of the engine increases.This will cause less fuel mixture to enter the cylinder, because thetime for it to get in becomes less, and the compression will thereforedecrease and the lines 41 and 52 will spread out bringing the line 49nearer the electrodes, as indicated in Figure 7, and thus effectively`advancing the ignition, which again is what is desired under thiscondition.

Decreasing the speed has the opposite effect, increasing the compressionagain and crowding the stratified mixture into the space, as indicatedin Figure 6, thus effectively retarding the ignition.

It will be seen that the position of the critical region of stratifiedfuel mixture will be governed by a number of factors. These are: (l) thenormal compression in the cylinder at the end of the compression stroke;(2V) the normal engine 8 speed; (3) the size of the firing space 46; (4)the shape of the firing space 46; and (5) the amount of oxygen (air)admitted to the firing space 46 prior to compression.

The shape and size of the space 46 and the amount of oxygen (air)admitted to the space may be controlled for any given engine. I havefound that a convenient shape and size may be determined by the innerend of the spark plug, and I control the amount of air admitted by thesize of the duct and the arrangement of the valve.

In variable speed, variable load, internal combustion engines now inuse, the automatic advancing and retarding of the spark is usuallyaccomplished by two automatic mechanical adjusting devices operating onthe distributor, one under control of the suction in the carburetor orintake manifold and the other controlled by centrifugal force. I havefound that the automatic effective adjustment of the spark which myinvention provides may be used to replace entirely the mechanicaladjusting devices referred to above, or the invention may be used inconjunction with these mechanical adjusting devices. In either case theadded advantage is obtained of causing substantially instantaneous andcomplete combustion of the fuel mixture at a time when it will do themost good, so that the eliiciency of the engine is greatly increased.

The embodiment of the invention illustrated in the figures thus fardescribed is suitable for use in an automobile engine equipped with theusual controls for advancing and retarding the spark and having a normalcompression of pounds per square inch. Good results have been obtainedwhen the various dimensions were as follows:

Threads on shell to fit engine millimeters. Internal diameter of end ofshell 9- .2813 inch. Internal diameter of shell 9 at portion 18 .355 to.360' inch. Internal diameter of barrel at 26 .263 to .271 inch.

14 millimeters x 11,1

Diameter of inner end of insulator" .1625 inch Diameter of inner end ofinsulator adjacent enlarged portion .2188 inch. Distance of electrodegap to end of barrel 19 .31 inch. Threads on barrel forming duct 45-- 10millimeters x 1 millimeter. Pitch diameter of thread .3675 to .3642millimeter. Distance from end of barrel to valve chamber .1875 inch.Thickness of valve ring .O15 inch. Clearance between valve ring and.Shoulder 15 .010 Diameter of holes 43 .040 inch. Width of space 44between barrel 19 and shell 9 .004 to .O08 inch. Gap between electrodes.018 to .025 inch. Spacing of distributor points .012 inch.

Although the duct l5 around the threads between the firing space 45 andthe valve chamber 38 has a very small cross section, it allows enoughair to pass through to obtain good results with an engine having dualmechanical spark controls at the distributor, as explained above. Inaddition, the burned gases are prevented by the cross section and lengthof the duct from being forced into the valve chamber by the explosionand thus the spring 40 is protected. In some in stances, I may stillfurther protect the spring against hot gases by providing a sleeve 53,preferably of stainless steel to fit loosely over the threaded end ofthe barrel le within the spring 46, this sleeve being provided with ahole or holes 5l! for the passage 0f air.

The plug, as described, may be inserted in an engine cylinder in placeof the ordinary plug,

without any other change, resulting in much bet- .ter operation of theengine. However, I have found that because the fuel is used moreefficiently', much less is needed under all conditions of engineoperation. I may therefore obtain better mileage by reducing the size ofthe main jet by a larger metering rod to produce a leaner mixture whenthe main jet is in operation.

I have also found that in adjusting .the engine for optimum operation,itis best to set Athe timing in accordance with standard practice andthen advance the setting until the most power is obltained withoutpre-ignition. When properly adjusted, an automobile can start at-tenmiles .an hour at the bottom of a thirty degreegrade yand with thethrottle lwide open pick up speed smoothly and without pre-ignitionordetonati'on. If the car fails to pick up speed, the settingef thespark should be advanced; if pre-ignition occurs, the setting of thespark should be retarded.

Best results have been obtained with regular gasoline, that is gasolinewhich has not been treated with tetraethyl lead or the like.

The results obtained with the invention are startling. I have foundafter repeated tests that the mileage per gallon of any automobile `canbe increased by at least ten percent and with one standard automobile ofa well known make, I have increased by 50% the mileage per gallon statedby the manufacturer to be the standard mileage of the car.

In addition to the increase of mileage which comes with the practice ofthe invention, other phenomenal results are obtained. These may belisted as: increased power and therefore increased acceleraticn; cooleroperation of the engine, and especially cooler operation of the sparkplugs with accompanying long life thereof; slower idling speed for theengine at much smoother operation than with ordinary engines; much lesstendency for carbon to form in the cylinder or around the electrodes ofthe plug, since the combustion is substantially complete and thereforeless fouling of plugs and valves.

In addition to these advantages the whole` engine may be designed toincorporate the invention with the result that the compression may beraised; a longer stroke may be used with no loss in revolutions perminute; and there need be no limit to the bore of the cylinder.Heretofore, gasoline engines have been limited to a six inch diameterbore. Beyond that diameter the combustion becomes very inefcient. Withthe use of the invention, however, the' efficiency o'f engines withbores larger than six inches can be increased several hundred per cent.Also an engine designed in accordance with the invention permits the useof a smaller cooling system than required w' the ordinary engine and alower powered ignition system.

The size of the duct leading from the valve chamber to the firing spaceforms an important control for the amount of oxygen admitted Ato thefiring space during each cycle of the engine, but the amount of thisoxygen may be additional- Yly controlled by the pressure of the springe9 restricting this opening, less of the mixture can get into the:firing space, with the result that the stratification as indicated inFigure 7 will be approached. One manner of restricting this opening hasbeen illustrated in Figures 8 and 9. Here the shell 55 is provided witha disc 5t which is welded over the open end thereof. This disc serves asthe grounded electrode of the plug and is provided with ,a hole 157into' which the center electrode 5,8 extends, the hole beingsufficiently large to provide the desired spark gap between the Ydiscand the center electrode. If less restriction ,fis desired, the hole 5.1may be elongated or additional holes may be provided in the disc.

As has `been stated above, the variation in position of thevstrati-,fied fuel mixture in the ring space file, under control of thecompression, provides an automatic adjustment of the effective timing ofthe spark. The embodiment -already described may be used with enginesprovided with lmechanical spark advance apparatus. ,An embodiment of theinvention will now be described by means of which the mechanical sparkadjusting devices on an engine may be entirely eliminated and the timingof the spark permanently set at vabout ,dead center position of thepiston.

The arrangement is illustrated in Figures 10 vand 11 in which the plugshown is generally the same as that already described, having a shelle5, much the same as the shell 9 of Figure 1, and a barrel -E whichcorresponds to the barrel l!! of Figure l. But the yfiring space 6l hasbeen made longer and narrower than that of Figures l to 8.

'I'he barrel t6 differs from that of Figure 1` in that the inner end t6is extended to be flush with the inner end ofthe shell 65, and bothparts have extending cooperating threads. A groove it is provided in theouter surface of barrel fi midway betweenthe end of the barrel and thevalve chamber le, this valve chamber being identical with that describedin connection with the other figures. The threads between the groove Si?and the -end of the barrel 5% are standard and engage vin the normal waywith the threads of the shell. Ilrhe threads ll, however, between thegroove S9 andthe valve chamber 'iii are flattened, as by machining offthe peaks of the threads, so as to increase the clearance and provide aduct ll2 of Igreater cross section than the `duct 45 of Figures ldand 2for the air to pass between the-groove 69 and the valve chamber le.l-Ioles i3 are provided through the barrel between ,the groove ,69 andthe interior space vel. Preferably two holes are provided diametricallyopposite each other, although more `may be provided if desired.

With the arrangement vjust described, it will `be seen that there ismuch freer access of air from the valvechamber 10 to the space Si' thanwas provided in the structure of the other gures. Because 'of the groove69 and the flattened threads on thebarrel, the structure is ksomewhatweaker, and I overcome `this by providing an extended rim k714 attheouter end of the shell S5 and spinning this krim over-the outer endof the .barrel whenassernbling. Holes l5 are drilled at spaced pointsaround the ycircumference of the rim to give vaccess lfor the air to thespace 'lebetween the barrel and theshell.

In the voperation of this plug, hot gases may pass into thegrooveeithrough theholes '13, and 4in order ,to prevent damage from heatto the spring and the valve inthe valve chamber, which :Will beunderstoodto befthe same as those yshown in connection wththeotherngures, I provide in the -groove 69 a sleeve 11 which may be a splitring of stainless steel and may snap loosely over the narrow portion ofthe groove and t loosely therein. Gases impinge on the sleeve and aredisbursed and cooled before entering the valve chamber.

Because the space 6'? is longer and narrower than the space 46 ofFigures 1 to 8, the stratification of the fuel mixture becomes moresensitive to changes in compression, and hence the automatic adjustmentof the spark timing is obtained. A long narrow space will also produce amore Violent blow-torch eiect than a shorter wider space, causing acloser approach to instantaneous combustion in the main combustionspace. By carefully designing the ring space for a particular engine thedesired result can be obtained.

Where more air is needed in the space 46 or the space B1, in order tobring the critical region in the fuel-air mixture nearer to the pointwhere the spark is produced, I may mill away a portion of the threads onthe barrel, as shown at 'i8 in Figures l2 and 13, to increase the crosssection of the air duct still further.

It is the oxygen in the ring spaces d6 and El which permits me tocontrol the flame propagation, as explained above, and this oxygen issupplied by a pair in the embodiments already described. However, itwill be apparent that in some instances it may be desirable to supply agas more nearly approaching pure oxygen, or under pressure other thanatmospheric. For instance, the engine of airplanes will require air orperhaps pure oxygen at a pressure higher than the surroundingatmosphere. To meet such a requirement, I may use the embodiment of theinvention shown in Figures 14- and l5.

In Figure 14, the inner part of the spark plug towards the combustionspace may take the form of either of the embodiments heretoforedescribed, except that the end which screws into the engine ispreferably longer, and this inner part is not shown in detail. In thisligure, the shell 'i9 and the barrel 8&3 correspond to the shells andbarrels of the other figures. lThe outer end of the shell 'i9 isprovided with a rim 8i which is spun over the outer end of the barrel3G, not only to make a more rigid connection, but also to make a gastight seal at the outer ends of the shell and barrel. The gland nut 82which holds the central insulator 83 in place is extended in a sleeve 84which is provided at its outer end with threads S5 to receive a suitablefitting S6 at the end of a -flexible hose 81 leading from asupercharger, (not shown) or other source of the gas to be fed throughthe spark plug. The outer surface of the enlarged portion 88 of theinsulator 83 is provided with a plurality of radial grooves 89 whichalign with a groove Sil formed circumferentially in the inner wall ofthe barrel 8i). A plurality of radial holes 9| are provided through thewall of the barrel to connect the groove $56 with the cylindrical duct92 formed between the barrel and the shell.

The inner end of the gland nut 82 may also be provided with radialgrooves 93 so that when the nut is screwed down against the surface ofthe central insulator with the usual soft metal gasket, the grooves 89and 93 provide passage into the groove 9B and holes 9|.

A ceramic sleeve 9A is provided within the gland nut 82 which ts snuglyagainst the inner wall of the sleeve 84 of the nut and is thin enough toprovide an air passage between its inner wall and the central insulator83. This ceramic sleeve may be held in place by spinning the outer endof the gland nut over it as indicated at 95 in the drawing. The innerend of the sleeve 94 may also be provided with a plurality of grooves 96to insure a passage of gas from the inside of the sleeve into the grooveand thence to the duct 92.

The electrical connection may be made to the plug by means of anignition wire 91 extending down the center of the hose S1 into thesleeve 94. The ignition wire may have a spring 98 at its end whichcontacts with the outer end 99 of the center electrode at the outer endof the insulator.

Except for the fact that the gas (air or oxygen) is delivered to theplug from a desired source and may be under pressure, the plug ofFigures 14 and l5 operates in the same manner as the other embodimentsalready described.

It will be noted that the insulator in the different embodimentsillustrated ends some distance from the end of the central electrodewhere the spark is produced, this construction being different from thatof the ordinary spark plug where the insulator is carried almost to theend of the electrode. This provides the necessary increased volume forthe firing space, and I have found that the exposed portion of theelectrode is unaffected by the burning gases 'because of the coolingeffect of the incoming air. To decrease the size of the firing space,the insulator may be carried to the end of the shell.

In the embodiments shown, the gap between the electrodes is about flushwith the inner wall of the engine head. It is to be understood, however,that with a given amount of air entering the plug, the timing of theflame movement from the gap to the critical region of the gas mixturemay also be varied by moving the gap into or out of the firing space.The position of the gap will therefore be determined by the particularrequirements.

While the use of the invention in connection with a four cycle enginehas been described in detail, it will be understood that the inventionis by no means limited to any particular typev of engine, but may beused wherever a more accurate control of ilame propagation is desired.

Modifications of what has been shown and described may 'be used withoutdeparting from the spirit of the invention and I do not wish to limitmyself except by the appended claims.

What I desire to claim and secure by Letters Patent is:

1. A spark plug comprising a body member, means at one end of saidmember for attaching said member in the cylinder head of an internalcombustion engine, electrodes at the same end of said member providing aspark gap, an insulator extending axially through said body member, aconductor extending through said insulator and forming one of saidelectrodes at its end, said body member having a cavity outside saidinsulator communicating with the space adjacent said gap and on theopposite side of said gap from the combustion chamber of said engine, aduct leading from said cavity to the outside of said plug through saidmember but outside of said insulator, and a one-way valve in said ductpermitting gas to pass into said cavity through said duct but preventingpassage in the other direction, the configuration and size of saidcavity, the cross section of said duct, and the sensitiveness of saidvalve lbeing such that stratification of the normal fuel mixture and thegas in- 13 troduced through said duct will occur in said cavity duringthe compression stroke of said engine, so as to control the flamepropagation in the combustion chamber thereof for different speed andload conditions of said engine.

2. A spark plug, as defined in claim 1, in which the duct has anenlargement forming a valve chamber in which the valve operates.

3. A spark plug, as defined in claim 2, in which the valve chamber isannular, the valve is a thin, at, annular plate, and a coil spring isprovided for normally holding said valve against its seat, and in whichshielding means is further provided in said valve chamber to protectsaid spring from Vhot combustion gases.

the valve chamber and inv which the threads on one of the parts areattened to increase the cross section of the duct into the valvechamber.

6. A spark plug comprising a body member, means at one end of saidmember for attaching said member in the cylinder head of an internalcombustion engine, electrodes at the same end of said member providing aspark gap, an insulating member extending axially through said bodymember, a conductor extending through said insulating member and formingone of said electrodes at its end, said body member having a cavityoutside said insulating member communicating with the space adjacentsaid gap and on the opposite side of said gap from the combustionchamber of said engine, a duct leading from said cavity to the outsideof said plug through said member but outside of said insulating member,and a one-way valve in said duct permitting gas to pass into said cavitythrough said duct but preventing passage in the other direction, theconfiguration and size of said cavity, the cross section of said duct,and the sensitiveness of said valve being such that stratification ofthe normal fuel mixture and the gas introduced through said duct willoccur in said cavity during the compression stroke of said engine, so asto control the ame propagation in the combustion chamber thereof, saidbody member being formed of two telescoping parts having threadedengagement at the inner end of the spark plug, said parts beingrelatively displaced beyond said threaded portions to define a chamberfor said valve and the threaded connection between said parts providinga tortuous, restricted portion of said duct between said valve chamberand said cavity.

7. A spark plug, as defined in claim 6, in which the two telescopingparts extend outwardly of the plug a relativley long distance in closelyspaced parallel relationship, forming an annular passage of small crosssection between the valve chamber and the outer end of the plug.

8. A spark plug, as defined in claim 7, in which one of the telescopingparts has a groove in its wall opposing the other part, adjacent thevalve chamber, a filter is provided in said groove, and a duct isprovided in said part extending from said valve chamber to said grooveand forming the inlet duct for said valve chamber.

BERNARD C. FISHER.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,218,215 Schlundt Mar. 6, 1917 1,246,890 De Vilbiss Nov. 20,1917 1,409,400 Peterson Mar. 14, 1922 1,555,718 Schroeder Sept. 29, 19251,605,381 Wirrer Nov. 2, 1926 1,722,404 Whatmough et a1. July 30, 19291,816,432 Hill July 28, 1931 1,960,344 Muir May 29, 1934 1,963,801OMarra June 19, 1934 2,153,598 Steward Apr. 11, 1939 2,459,286 RabezzanaJan. 18, 1949 FOREIGN PATENTS Numb er Country Date 345,528 Great BritainMar. 26, 1931

